1. Field of the Invention
The present invention relates to a light emitting device package and a method for manufacturing the same, and more particularly, to a light emitting device package capable of emitting uniform white light and a method for manufacturing the same.
2. Discussion of the Related Art
Light emitting diodes (LEDs) are well known as a semiconductor light emitting device which converts current to light, to emit light. Since a red LED using GaAsP compound semiconductors was made commercially available in 1962, it has been used, together with a GaP:N-based green LED, as a light source in electronic apparatuses, for image display.
The wavelength of light emitted from such an LED depends on the semiconductor material used to fabricate the LED. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material representing energy difference between valence-band electrons and conduction-band electrons.
A gallium nitride (GaN) compound semiconductor has been highlighted in the field of high-power electronic devices including light emitting diodes (LEDs) because it exhibits a high thermal stability and a wide band-gap of 0.8 to 6.2 eV. One of the reasons why the GaN compound semiconductor has been highlighted is that it is possible to fabricate semiconductor layers capable of emitting green, blue, and white light, using GaN in combination with other elements, for example, indium (In), aluminum (Al), etc.
Thus, it is possible to adjust the wavelength of light to be emitted, in accordance with the characteristics of a specific apparatus, using GaN in combination with other appropriate elements. For example, it is possible to fabricate a blue LED useful for optical recording or a white LED capable of replacing a glow lamp.
Such a white light source may be fabricated using LEDs for emitting light of three primary colors, namely, red, green, and blue, or using an LED for emitting light of a certain color and phosphors.
In accordance with the method, which uses phosphors, a white light source may be fabricated using a blue LED and yellow phosphors. In this case, white light is produced as blue light emitted from a blue LED and yellow light emitted from yellow phosphors excited by the blue light are mixed.
Similarly, the white light source may be fabricated using a green LED and red phosphors or using an ultraviolet LED and red, green, and blue phosphors.
In accordance with the method, which uses a blue LED and yellow phosphors, to fabricate a white light source, red light and green light are emitted as blue light emitted from the blue LED is absorbed in the yellow phosphors in certain degrees. The red light and green light are mixed with the blue light not absorbed in the yellow phosphors, so that they are viewed in the form of white light to the observer.
The above-mentioned method, which uses a blue LED and yellow phosphors, to fabricate a white light source, are widely used because the fabricated white light source exhibits excellent color rendering, high stability, and high reliability.
FIG. 1 illustrates an LED lamp which emits white light using the above-mentioned LED and phosphors.
In the illustrated LED lamp, a blue LED 3 is disposed on a stack 2 mounted in a reflective cup 1. A filler 5, which is formed by mixing phosphors 4 with a silicon gel or an epoxy resin, is filled in the reflective cup 1 such that the filler 5 encloses the blue LED 3. A glass 6 is arranged over the filler 5.
In this LED lamp structure, however, the filler 5 enclosing the LED 3 may have a non-uniform thickness. For this reason, there may be an optical path length difference between light paths a and b of light emitted from the LED 3 to the surface of the glass 6.